Credit: The Associated Press

FILE - In this Dec. 15, 2017, file photo, President Donald Trump sits with Attorney General Jeff Sessions during the FBI National Academy graduation ceremony in Quantico, Va. Trump’s White House counsel personally lobbied Attorney General Jeff Sessions to not recuse himself from the Justice Department’s investigation into potential ties between Russia and the Trump campaign. (AP Photo/Evan Vucci, File)

WASHINGTON — President Donald Trump's effort to keep Attorney General Jeff Sessions, a vocal and loyal supporter of his election bid, in charge of an investigation into his campaign offers special counsel Robert Mueller yet another avenue to explore as his prosecutors work to untangle potential evidence of obstruction.